In networks, a transmitting node may use carrier sensing to determine if a shared medium is available so as to avoid packet collision. In a wireless network, the two types of carrier sensing typically used are physical carrier sensing, by the physical layer that samples the radio-frequency (RF) energy level in the medium, and virtual carrier sensing, by the media-access control (MAC) layer that updates a node's network allocation vector. A node maintains a network allocation vector to indicate the period(s) during which the medium is reserved by other nodes; hence, it knows when not to transmit.
When contending for the medium, a node broadcasts its intended transmission period. Each node that receives the broadcast updates its network allocation vector. When implemented correctly, the use of network allocation vector may reduce the power consumption needed for frequent sampling of the medium. Unfortunately, the mechanism for maintaining network allocation vectors in current networks typically requires that a node accurately decode a control frame, sent either by the transmitting node or the receiving node, which contains the network allocation vector information. If for any reason the node fails to decode the control frame, its network allocation vector will be inaccurate.